The function of GCNT2 (glucosaminyl (N-acetyl) transferase 2 (I blood group), ENSG00000111846) is as follows. Branching enzyme that converts linear into branched poly-N- acetyllactosaminoglycans (PubMed:12424189, PubMed:8449405). Introduces the blood group I antigen during embryonic development. It is closely associated with the development and maturation of erythroid cells. {ECO:0000269|PubMed:12424189, ECO:0000269|PubMed:7579796, ECO:0000269|PubMed:8449405}. [Isoform C]: Determines the expression of the blood group I antigen in erythrocytes. .